Multiple element electroacoustic transducer



June 28, 1960 R. L. STEINBERGER ETAL MULTIPLE ELEMENT ELECTROACOUSTIC TRANSDUCER Filed April 27, 1950 5 Sheets-Sheet 1 lllll 3mm R. L. STEINBERGER R. J. COLSQN HAROLD L. SAX TON I? mm June 28, 1960 R. L. STEINBERGER ET AL 2, ,297

MULTIPLE ELEMENT ELECTROACOUSTIC TRANSDUCER Filed April 27. 1950 5 Sheets-Sheet 2 awed/M014 R. L. STEINBERGER R. J. COLSON HAROLD L. SAXTON ATTORN EYS R. L. STEINBERGER ETAL MULTIPLE ELEMENT ELECTROACOUSTIC TRANSDUCER Filed April 27, 1950 June 28, 1960 5 Sheets-Sheet 3 R. L. STEiNBERGER R. J. COLSON HAROLD L. SAXTON June 28, 1960 R. L. STEINBERGER ErAL 2, 43,297

MULTIPLEELEMENT ELECTROACOUSTIC TRANSDUCER Filed April 27. 1950 5 Sheets-Sheet 4 E m M O 0 f" m X A d NM N ls mun z 5 SCL Au LJR ..A Dun-"H6 w 3 3 June 28, 1960 R. L. STEINBERGER ETAL 2,943,297

MULTIPLE ELEMENT ELECTROACOUSTIC TRANSDUCER Filed April 27, 1950 5 Sheets-Sheet 5 GANG PROTECTING DEVICES RECEIVERS QUADRANTIALLY SPLIT TRANSDUCER INVENTORS R. L.STEINBERGER R. J. COLSON HAROLD L. SAXTON ATTORNEYS United States Patent MULTIPLE ELEMENT ELECTROACOUSTIC TRANSDUCER Raymond L. Steinberger, Alexandria, Va., Robert J. Colir in, Washington, D.C., and Harold L. Saxton, Friendly,

Filed Apr. 27, 1950, Ser. No. 158,580

=4 Claims. c1. 340-4 (Granted under Title 35, U.S. Code (1952), sec. 266) or in one or more of four partsindependently of each other.

Another object is to provide a transducer adapted to be used either as an efiicient beam projector-receiver or as a bearing deviation indicator. Another object is the provision of a multi-element electrosonic transducer capable of operation as two or more spaced receiver elements without detriment to operation of the entire device as a single, large, continuous surface transmitting diaphragm. Another object is to provide a transducer having a plurality of independently operable sector shaped portions closely juxtaposed to form substantially a single effectively solid circular diaphragm.

Another object is to provide a transducer construction particularly adapted to the utilization of piezoelectric crystal elements.

Another object is to provide a piezoelectric crystal transducer constructed in the form of a compact circular array of crystal elements with provision for the'necessary freedom of limited transverse expansion and contraction without displacement of the constituent elements.

A further object is the provision of a compact circular array of piezoelectric crystal elements in which certain sectors of the circular array are operable independently of each other and without interference with each other. Various other. objects and advantages of the invention will become apparent from a perusal of the following specification and the accompanying drawings in which: Fig. l is a plan view of the device as mounted on the back plate, with other parts of the device omitted for the sake of clearness. f Fig. 2 is a detail, fragmentary top view of a portion of Fig. 1 enlarged to show the several layer structures including the metal plating on the individual crystal slabs. Fig. 3 is a perspective view of one quadrant partially assembled.

Fig. 4 is a side view partially in diametrical cross 7 section, of the complete device with the crystal array omitted for the sake of clearness, the section being taken on a diameter indicated by the line 44 of Fig. 1.

Fig. 5 is a prospective (side) diagrammatic view showing the multiple connecting strips.

Fig. 6 is an enlarged fragmentary detail showing in plan the terminal connections.

Fig. 7 is an enlarged fragmentary section on the line 7-7 of Fig. 6, and

Fig. 8 is a side view of the completed device with the casing removed and the peripheral binding tape partly broken away.

Fig. 9 is an enlarged fragmentary perspective view, showing the structure of the sandwich strips.

.bling Within the case.

Patented June 28,

Fig. 10 is a small scale perspective view of the complete device.

Fig. 11 is a fragmentary section on the line 11-11 of Fig. 1, showing the position of the filler pipe.

Fig. 12 is a circuit diagram of a system employing the improved transducer.

Fig. 1, which is a front view of the transducer with the casing removed, shows the complete, substantially circular array of piezoelectric crystal slabs 10' arranged in cubicle crystal group elements 11 each crystal group element constituting an assembly of four of the crystal slabs. The individual crystal slabs are of the type known as X-cut crystals having their major faces conductor coated as is usual in the art, which conductor coating is indicated at 12 in the enlarged Figure 2.

While in Fig. 2 this conductor coating has been shown as of substantial thickness for the sake of cleamess,"i't is to be understood that in practice it is an extremely thin plating applied in any known or other suitable manner as by sputtering. In assembling a group element 11 the four crystal slabs are arranged with their coated faces of opposite polarity in contact thus electrica-lly connecting the crystal slabs in series.

The group elements 11 are arranged in parallel rows, the number and length of the rows being such as to provide the maximum number of groups 11 capable of inclusion within a given circle. In each row the groups are arranged with the uncoated sides 13 of the groups in proximity but separated by cork strips 14, and with the outermost coated sides of like polarity on one side of the row so that all the group elements in a given row have the same polarity on one side of the row and the opposite polarity on the other side. By the term sides of like polarity is indicated corresponding sides of difierent crystal groups which have like polarity for a given condition of pressure relative to the crystal axes. For example, according to one convention, in an elongated X-cut crystal slab, the major side which assumes a plus charge in response to longitudinal compression is called the, plus side.

As indicated in- Fig. 2 the group elements 11 of a given row are separated by short strips 14 of suitable, non-conducting, elastic material such as cork preferably impregnated with wax or rubber, while the adjacent rows are separated by sandwich strips 15 each composed of a central strip 16 of resilient sound insulating material such as that of the strips 14, a pair of thin relatively hard electric insulating strips 1718 one on each side of the cork strip and a pair of metallic electrode strips 19-20 one on the outer side of each insulating strip.

For a more detailed disclosure of the assemblage of elements attention is directed to Figs. 2 and 3. Here Fig. 3 shows a quadrant of the circular array before assem- Here it will be seen that there are six rows of the group elements 11, the group elements in each row being separated by the short strips or slabs 14 of cork, while the rows are separated by the sandwich strips 15 described above. For a clearer showing of the top edge view of the sandwich strips reference is to be had to Fig. 2 drawn on a scale sufiiciently large to show the various layers of material in appreciable thickness. Because of the scale on which Fig. 3 is made it is impossible to show actual thickness to certain of the elements of thin sheet material such as shown in Fig. 2 for the Bakelite strips 17-18, electrode strips 19-20 and the conductor coating 12 on the crystal elements 10, these elements are shown in a single line in Fig. 3 for the sake of clearness, the showing in Fig. 2 being relied upon for a more definite disclosure of their physical re lations. The several rows are arranged with like polar ities adjacent so that the electrode strips on opposite faces of the intervening sandwich strip may be of the same polarity. Thus one set of alternate sandwich strips have all their electrode strips of one polarity, while the other set of alternate strips have all their electrodes of the other polarity. .In as much as the outside rows have no adjacent rows beyond them only a partial sandwich strip is required such as is shown opened out at the forward end of the sector of Fig. 3, such end cover strip being designated as a whole at21. For the composition of the short end strips which are alike, reference may be had to the strip 21 which is comprised of an electrode strip 22, a strip 23 of hard insulating material such as Bakelite, and a cork strip 24, which latter may be of the impregnated type mentioned above. In the complete assemblage the cover strip 21 assembled'in the order shown in Fig. 3-is placed together up against the end row with the conductor strip 22 in contact with the conductor coatings 12 on the outer faces of the end row of crystal groups 11 as clearly shown in the enlarged detail view ofFig. 2. Current is led to and from the conductor strips 19, 20 and 22 by way of extension tabs 25. From Fig. .3 it will be noted that the extension tabs at 25 of opposite polarities are grouped in different horizontal .planesone above the other. In the present instance those of one polarity extend outwardly in the lowerplane while those of the opposite polarity extend outwardly in an upper plane. As will later be described, those in the upper plane extend to a common buss connection individual to the quadrant while those in the lower plane connect to a buss connection common to all four quadrantsconstituting aground or common return connection for the whole assemblage. One radial edge of the quadrant is covered by a non-conducting strip 26, here shown as a single strip because of the thinness of its constituent layers relative to the small scale of the diagram. For "a more detailed disclosure of the strip 26, reference is to be had to the enlarged iiragm-entary perspective view, Fig. 9 which shows the strip as consisting of a central strip 27 of resilient sound insulating material such as cork of thetype mentioned above, and two outer facing strips 28 of relatively hard electric insulating material such as Bakelite. The other radial edge of the quadrant of Fig. 3 is covered by a long sandwich strip 29 similar in all respects to the sandwich strips 15 (Fig.2) except that it runs the full diameter of the complete circular assemblage as indicated in Fig. 1, and the central cork strip is wider, for example in the present embodirnent, one-eighth of an inch as compared with one-sixteenth of an inch for the intermediate sandwich strips 15 and the end sandwich strips 21. Similarly, the cork strip :26 is of the same thickness as the'cork strip in the sandwich strip 29. To complete a continuous 'arcuate edge .for the quadrant suitable filler blocks 30, 31, 32, 33 and 34 of insulating material such as Bakelite or other suitable phenolic material are provided.

The assemblage of crystals constituting four of the quadrants as shown in Fig. 3 are securely cemented to a back plate 35 (Figs. 4, and 7) through theintermedi ation of a thin disk '36 (Fig. 7) of hard insulating material such as Bakelite, the disk being securely cemented to the back plate while the lower faces of the crystals, the filler blocks and the spacing strips are securely cemented to the disk. The cement used may be of any known or other suitable kind, preferably a firm setting rubber cement such as is known at the present time under the name V-ulcalock. The back plate may' be of any known or other suitable metal or metal alloy, inthe present instance steel.

For the sake of clearness the crystal assemblage is omitted from Fig. 4. However, it will be clear from the large scale fragmentary cross section, Fig.7, how the crystal assemblage occupies the space between the back plate 35 and the windowed casing 37. As indicated in 4 and 7 the windowed casing 37 is comprised, in the main of av metal, annular side wall member 38 across -the firontiof which is formedtheenclosing sound-window element 39 extending over and secured to the front edge portion of the casing side wall 38. The window element 39 is constructed of a material transparent tounderwater sound. This material should be one having substantially the same acoustic qualities as sea water in other words, substantially the same velocity of propagation of compressional wave energy as sea water. In the present instance the material is rubber, vulcanized to the side wall 38.

Referring to Fig. 5 it is to be understood that this is not a true perspective view'but a perspective diagram in which any attempt to indicate thickness of certain sheet material has been omitted for the sake of clearness in the showing of the general relation of'parts, a more detailed disclosure of the structure being obtainable from the various enlarged detailed illustrations, which latter are necessarily somewhat distorted to show appreciable thickness in the various extremely thin sheets and layers. As indicated in Fig. 5, the four quadrant sectors are secured to the back plate 35 with their radial edges juxtaposed to form a circular assembly, the various filler blocks such as the blocks 30 to 34, and similar blocks 30' to 34', for alternate quadrants in the form of mirrored images of the'former, being placed as indicated here and in Fig. 3 to complete the true circular periphery. The circular assembly thus formed is bound around the periphery with the belt 40oi5suitable thin hard insulating material such as phenolic material, in the present case Bakelite. Slots .41 in this belt provide openings through which the circuit connecting tabs 25 from the various conductor plates extend for connection with buss connecting strips 42, 43, 44, 45 and 46 placed aroundthe outside of the belt. .All of the lower tabs are of one polarity and extend through to the ground or common return buss 42 to which they are connected as by soldering as indicated at 47. The tabs in the upper plane are of a polarity opposite to that of the lower plane tabs. Those of the upper tabs 25 which extend from the quadrant designated as a whole as 50, are connected to the buss band 44, to which they are soldered as indicated at 51. Similarly the upper tabs firom quadrant 48 connect to buss 45, those from quadrant 49 connect to buss 46 and those from quadrant 57 connect to buss 43. Reference to Fig. 6 -will explain how the five buss bands connect individually with terminal screws on the short filler blocks 32, 33, the 'busses 42, 43, 44, 45 and 46 being connected to terminal screws 52, 53, 54, 55 and 56 respectively.

As shown in Fig. 8, the crystal assemblage on the back plate 35 is completed by application of an insulating tape 58 covering the belt 40 and the various buss strips. Thus is completed the crystal assemblage ready for mounting on the back cover plate 59. Electrical connection is made with the terminal screws 52 to 56 as indicated in Fig. 7 through the multiple conductor cable 60 entering through a bore 61 in the filler block 33 to permit its several conductors to be connected to their respective terminal screws as indicated for the conductor 62 and terminal screw 55. As indicated in Fig. 4 the cable 60 enters the interior of the device through loose fitting apertures in the back plate 35 and back cover plate 59 and a tight fitting aperture in a sealing gasket 63. Afiter the connections are made to the terminal screws, the space above the short filler blocks 32 and 33 is filled with parafiin or other suitable wax 64 (Fig. 1). The casing 37 is applied as shown in Fig. 4 and secured to the back cover plate 59 by an annular series of studs 65 threaded into the cover plate and drawn toward the back plate by nuts 66 to axially compress and radially expand the intervening annular sealing gasket 63 of rubber or rubber like material. An oil filler pipe 67 as shown in Fig. 11, provides means for filling the space between the casing and the crystal assemblage with an oil such as castor oil or other suitable liquid having substantially the acoustic qualities of sea water. A closure cap 68 seals the outer end of the pipe. The filler pipe passes through the gasket 63 into threaded engagement with the inside of an aperture in the back plate 35 which aperture is in register with a channel 69 in one of the filler blocks 30 or 31, Figs. 1, and 11.

The transducer above described is particularly adapted to use in systems where it is desired to receive compressional wave signals independently through two or more transducers at diflferent spaced points as in sound wave direction finding either in a single plane, or in simultaneous indication of azimuth and vertical bearing of a source of sound or a sound reflecting object, and to transmit simultaneously through a group of two or more of the same transducers to efiect transmission as from a single compressional wave generator of wider radiating surface than a single one of the difierent transducers.

For transmission of a common signal simultaneously through all four quadrants simultaneously and reception through each quadrant individually at separate receiver elements for determining of phase differences the transducer may be connected as indicated diagrammatically in Fig. 12. As here indicated the difierent quadrants may be connected individually each through an individual switching element of a gang switch to a common driver, the switching elements being operable simultaneously for connecting the driver to all the quadrants during sending, and for opening this connection to separate the quadrants from each other during receiving. The different quadrants may be permanently connected with their respective individual receivers through suitable pro tecting devices individual to the receivers as indicated. It will be understood that the outputs of the receivers may supply any known or other suitable system of direction indication.

Although certain specific embodiments of this invention have been disclosed and described it is to be understood that they are merely illustrative of this invention and modifications may, of course, be made without departing from the spirit and scope of the invention as defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In an electroacoustic transducer, a circular assemblage of piezoelectric crystal elements arranged to form a compact layer substantially evenly spaced and distributed over a circular area, said crystal elements being divided into four groups each forming a quadrant of the circle, the crystal elements of a quadrant group being arranged in rows with electrode strips extending along the sides of the rows, a strip of relatively soft electrically non-conducting resilient sound insulating material such as cork extending between the electrodes of adjacent rows, a strip of thin relatively hard electrical insulating material between each electrode and the strip of corklike material, and a connecting tab extending outwardly of the assemblage from each electrode strip.

2. An electroacoustic transducer as claimed in claim 1 having filler blocks of electrical insulating material arranged around the periphery of the assemblage of crystal elements to fill out a circular boundary circumscribing the crystal assemblage, and a wrapping of insulating tape binding together the assemblage of crystal elements and filler blocks.

3. In an electroacoustic transducer, a circular 2.8561111- blage of piezoelectric crystal elements arranged to form a compact layer substantially evenly distributed over a circular area, said crystal elements being divided into four groups each forming a quadrant of the circle, the crystal elements of a quadrant group being arranged in rows with electrode strips extending along the sides of the rows, a strip of relatively soft electrically nonconducting resilient sound insulating material such as cork extending between electrodes of adjacent rows, a strip of thin relatively hard electrical insulating material between each electrode and the adjacent strip of corklike material, a connecting tab extending outwardly of the assemblage from each electrode strip, a boundary belt of insulating material surrounding the circular assemblage of crystal elements having slots therein through which pass the connecting tabs to the outer surface of the belt, buss connecting strips extending around the outer surface of the belt one for each quadrant group and connecting with the tabs of a given polarity of its associated quadrant, and a common ground buss connecting strip extending around the outer surface of the belt for connecting to ground the tabs not connected to the first mentioned busses.

4. An electroacoustic transducer as claimed in claim 3 in which the crystal elements are mounted on a flat diskshaped back plate and a hoodlike casing is provided in the form of a short cylinder open at one end and closed at the other end by an underwater-sound transparent window, the open end fitting around the periphery of the disk-shaped back plate and having a radially inwardly extending shoulder bearing on a peripheral marginal portion of the back plate, together with a back cover plate extending radially beyond the periphery of the back plate to overlap the rim of the open end of the casing, whereby removal of the hoodlike casing will expose the back plate clear of any side enclosure to facilitate construction and repair of the crystal assemblage.

References Cited in the file of this patent UNITED STATES PATENTS 2,076,330 Wood et a1. Apr. 6, 1937 2,384,465 Harrison Sept. 11, 1945 2,416,314 Harrison Feb. 25, 1947 2,417,830 Keller Mar. 25, 1947 2,427,062 Massa Sept. 9, 1947 2,452,068 Peterson Oct. 26, 1948 2,480,535 Alois et a1. Aug. 30, 1949 2,521,642 Massa Sept. 5, 1950 2,524,180 Schuck Oct. 3, 1950 

